David Baldwin, a cyclist-activist, poses for a photograph just off the W&OD Trail in downtown Leesburg. (Katherine Frey/The Washington Post)

By the time David Baldwin cycled past the Lincoln Memorial and down the Mall on Sunday afternoon, he had already logged 3,500 miles on his bike since embarking on a cross-country ride nearly two months ago.

Just minutes before, as he was crossing the Potomac, three Marine helicopters — likely carrying the president — flew by overhead.

Welcome to D.C., Baldwin thought, as he scrambled to capture the moment on his GoPro.

Baldwin, 53, is cycling across the United States in a campaign called the “Pursuit Ride” to raise money for and awareness about the lack of employment opportunities for adults with disabilities. The money raised will help fund The Center, a Houston-based nonprofit for people with intellectual and developmental disabilities where Baldwin serves as a board member.

Baldwin’s expedition has taken him from the shores of Astoria, Ore., where he ceremoniously dipped his bicycle tires in the frigid waters of the Pacific Ocean to mark the beginning of the journey, which crossed 14 states. He and his crew of riders have cycled past the vineyards of Oregon, the strange and rugged topography of the South Dakota Badlands, the lakes of Minnesota, the rush-hour traffic of Chicago, the bucolic farmlands of Indiana and the rolling hills of Maryland.

David Baldwin, a cyclist-activist, left, rides with his wife, Maire, and Joudan Ellis, as he nears the end of a 3,500-mile, cross-country bike ride to raise awareness of adults with development disabilities. (Katherine Frey/The Washington Post)

With the journey set to culminate at Rehoboth Beach, Del., on Wednesday, the team has raised $12.5 million — tantalizingly close to its goal of $13.5 million.

“It was a crazy goal, and to think that we’ve come so close is just awe-inspiring,” Baldwin said. “We started with just a few volunteers. Today there are over a thousand people working on this project. We’ve had over 100 people ride with me.”

Baldwin, who is an engineer by training and the co-president of SCF Partners, an energy company, came up with the idea of a cross-country bicycle expedition a year ago. He had been lying in bed, sleepless and restless, worrying about the financial challenges confronting The Center. He got out of bed and went on an early morning bike ride to clear his head.

As he was pedaling, an idea dawned on him: Why not cycle across the country to raise money for The Center?

“In recent times, our financial status has gotten tighter and tighter,” Baldwin said of The Center. “The state of Texas turns down federal funds that are allocated to support our clients. . . . So the financial viability of our large organization is always in question.”

Across the nation, only 17.5 percent of people with a disability are employed, according to data released by the Bureau of Labor Statistics in June. About 8 in 10 people with a disability are not in the labor force at all.

“It’s an amazingly untapped workforce, and we need to as a country do a better job of getting them employed,” Baldwin said of adults with intellectual and ­developmental disabilities.

The challenges that The Center faces is compounded by the fact that Texas ranks near the bottom of the nation — 49th — in providing fiscal support for people with intellectual and developmental disabilities, according to a 2011 report published by the American Association on Intellectual and Developmental Disabilities.

In addition to raising much-needed funds, Baldwin used the Pursuit Ride to learn how different organizations in the country are helping people with disabilities. In brainstorming sessions, Baldwin and his team talked to other leaders in the field about the need for continued advocacy to address federal and state funding shortfalls; opportunities to build partnerships with other nonprofit groups and businesses; the need for greater entre­pre­neur­ship and innovation in their field; and other issues.

“We’ve learned that there are a lot of people out there doing amazing work to support people with intellectual and development disabilities,” Baldwin said. “We’ve also learned that over the last 20 or 30 years, the advances of organizations like The Center have helped people with [disabilities] live and work independently. Because of that, life expectancies have more than doubled.”

Since starting the ride all those miles ago, Baldwin has lost about 15 pounds. Averaging about 73 miles on riding days, Baldwin said he burns through some 6,000 calories. To ensure that he is properly fueling his body, he consulted with the Baylor College of Medicine in Houston for nutrition advice and computes his daily caloric input and output.

And just because he’s burning all those calories doesn’t mean he’s pigging out to his heart’s content: He still has to carefully plan his meals, focusing carbohydrates in the morning and proteins in the afternoon.

He has also grown very attached to his fiberglass road bike.

“I’ve even had dreams now about sleeping on my bicycle,” Baldwin said. “That’s probably not a healthy sign, but I’ve gotten very comfortable on my bike.”

Asked whether, with the campaign’s culmination hours away, he now thought of himself as an athlete or an activist, Baldwin answered neither.

“I think of myself as just lucky,” he said. “I got to take two months off from my desk job. I got to ride with hundreds of friends across the country. I got to help something that’s really important to my wife and I. And I got to meet people . . . and see the country in a way that almost nobody gets to see the country.”

For people considering a fundraising expedition, he had these words of advice: “Don’t wait.”

“The chance to break the monotony of what you do every day — really try to push yourself and do something that helps others — is something that you will remember for the rest of your life. This has been the greatest two months of my life,” he said.

“Everybody should plan a pursuit. The chance to help someone helps give you a chance to help yourself.”